Protective coating



Patted gept. E42

s. ATENT OFFICE EBO'EEC COATING James N. Tuttle, Newton, Mesa, asslgnor, by

assignments, to James N. Tattle, Nn,

Masa, doing business as Bustproofing and Metal Finishing Company, Cambridge, Mass.

4 No Drawing. Application March 26, 1940,

Serial N0. 326,050

proof by treatment with such reagents as phosphoric acid, oxalic acid, acidulated ferric oxalate and the like'compounds which chemically react with the surface of the article under treatment so as to form a coating consisting essentially of an insoluble ferric salt. In order to increase the effectiveness of such protective coating the inter stices or pores have been filled with various types of oils, waxes, lacquers, resins and other fillers,

usually of an organic nature, but such treatments have been found generally unsatisfactory as the fillers undergo deterioration when exposed to usual weather conditions and consequently fail to provide added protection to the coating for any appreciable length of time.

Aluminum, aluminum alloyarticles, and the like surfaces may be treated by electrolytic processes to provide a substantially insoluble oxide coating whichis capable of being colored either by dyeing, or-by depositing in the interstices of the protective coating colloidal substances such as copper, silver, gold or other inorganic substances in finely divided condition, the latter procedure being relatively expensive and producing only a very limited range of colors.

Non-ferrous materials, such as magnesium zinc, zinc base die-castings, zinc and cadmium coated articles, etc., may be treated with such reagents as phosphoric acid, oxalic acid, etc., to produce a relatively insoluble porous, crystalline surface receptive to various finishes. However, such surfaces are incapable of being colored except by the use of pigmented or opaque coating compositions which invariably produce a relatively thick film and which, in the case of small fittings, machine elements, etc.,- results in objectionable dimensional changes.

The principal objects of the present invention are to overcome the aforementioned objectionable features and to provide an efficient and economical method of improving the resistance of protective coatings and also of coloring such coatings. A more specific object is to provide a meth- Parkerizing, Granodine and Bonderizlng processes, and modifications thereof, produce insoluble phosphate coatings, and that other prior art processes such as the Loxal process, and modifications thereof, produce insoluble oxylate coatings, all of which are physically similar in that they consist essentially of an insoluble porous crystalline film-like structure formed on 'and integral with the surface of the treated metal.

In accordance with the present invention, me-

' tallic articles having a porous crystalline protective coating, such as produced in accordance with any of the above-mentioned processes, is first thoroughly cleaned, if necessary, so as to remove dirt, grease, etc. and the cleaned article is then immersed or otherwise treated with an aqueous solution .of a metallic compound capable of yielding a fiocculent or gelatinous precipitate, the treatment being such that the solution penetrates the interstices or pores of the protective coatings. In order to permit a quick and uniform penetration of the treating solution, a suitable wetting agent is preferably dispersed therein.

The treating solution may consist of one or more salts of a metal which readily react to form a fiocculent or gelatinous precipitate, such as an hydrous oxide or other compound having the same or similar physical characteristics. Accordingly, the term "fiocculent precipitate as herein used connotes only those precipitates which contain varying amounts of water adsorbed by their component particles (as distinguished from those precipitates, such as true hydrates, in which the water is chemically combined in definite stoichiometric proportions), and which on standing lose water spontaneously, thus causing the mass to assume a less gelatinous and more granular character, the transformation being accompanied by a marked decrease in solubility, adsorbabilityand the peptizability of the compound. After having'uniformly impregnated the protective coating with the treating solution, the article is then subjected to a further treatment which is effective to cause the formation of the fiocculent precipitate within the interstices of the protective coating, the nature of such treatment 0d which is generally applicable to metallic ar- ,ticles having a protective coating produced by processes such as those known to'the trade as Parkerizing, Bonderizing, Granodine, etc. Further objects will be apparent from a considera-- tion of the following description.

depending upon the ingredients and character of the treating solution. In some cases theformation of this fiocculent precipitate is effected by subjecting the article either to a slightlyelevated temperature, or to a reduced temperature.

or it may be necessary merely to permit the treated article to remain at normal temperature It is well known that the aforementioned for a sufficient period to effect spontaneous precipitation, depending upon the particular type of ingredients employed; whereas in other cases the treated article may be subjected to a reactive medium such as ammonia fumes, an alkaline solution, etc. which is effective to cause the formation of the precipitate. In all cases th precipitate is deposited within the interstices or pores of the protective coating and due to its flocculent character clings tenaciously to the walls defining the interstices.

The formation of the flocculent precipitate may 'or may not be effective to color the article under treatment, depending upon the composition of the precipitate. For example, if the ingredients used and the treatment employed result in the are, as a class, entirely suitable for use as mordents and color lakes for various types of dyes.

After having formed the precipitates within the interstices of the protective coating, or after having colored or dyed the precipitate, the article is then subjected to conditions effective at least partially to dehydrate the precipitate, and to this end the article may be subjected to an atmosphere of warm and/or dry air for a period sufficient to permit the major portion of the water carried by the precipitate to evaporate. The dehydration of the precipitate causes it to assume a more granular character, the transformation rendering it substantially insoluble and being accompanied by a marked decrease in its ad-' sorbability. The dehydrated precipitate thus produced not only seals the interstices or pores of the original protective coating but furthermore, being highly resistant to agents tending to destroy or impair the original coating, provides a supplemental protection which greatly increases the eifectiveness of the original coating.

A specific illustration of what is now considered a preferred procedure isas follows:

Example 1 A treating solution is prepared by dissolving 16 lbs. and 11 oz. of aluminum sulphate in 4 gallons of water at a temperature between 70 and 100 F. A solution containing-5 lbs. of com mercial sodium carbonate in 4 gallons of water is then slowly added to the aluminum sulphate solution with constant stirring, care being taken to dissolve the precipitate formed during the mixing. After the two solutions have been mixed and all precipitate dissolved, 10 grams of a suitable wetting agent, such as Alkanol (Du Pont) dispersed in about 3 pts. of warm water, may be added with constant stirring. In event any insoluble matter is present the mixture may either be filtered or permitted to stand so that the insoluble matter settles out, after which the solution may be decanted. A treating solution thus prepared breaks down or precipitates out a flocculent aluminum compound (hydrous aluminum oxide) either when heated to a temperature of 130 to 140 F. or by the addition of approximately three volumes of cold water. By I varying the proportion of ingredients the breakdown temperature and dilution necessary to effect precipitation may also be varied.

The article to be treated is first cleaned in any suitable manner, if necessary, and is then immersed in a treating solution for a period of about two minutes, the temperature of the treating solution being maintained between and F., although for certain articles the immersion period may be considerably reduced. As a general rule,-however, two minutes is usually adequate to insure a thorough and uniform impregnation of the protective coating by the treating solution. After impregnation the article is centrifuged at a low speed to remove excess treating solution from its surface, and if desired the article may be subjected to a current of warm air so as uniformly to dry the treated surface.

Following the partial drying of the article under treatment, but without removing the treating solution from its interstices, it is then subjected to one of the treatments presently to be described, each of which is effective to cause a precipitation of the hydrous oxide within the interstices of the protective coating.

The article may be immersed in water at a temperature of F. for thirty seconds or more, depending upon its size and shape, after which it is dried in any-suitable manner; or the article may be subjected to dry heat preferably above F. for two or three minutes; or the article may be subjected to ammonia fumes for a few minutes; or the article may be immersed in an alkaline solution such as ammonium hydroxide, sodium hydroxide or the like, and subsequently rinsed and dried.

If desired, the foregoing treatments may berepeated one or more times so as to insure a immersed in a dye bath after the hydrous oxide has been precipitated. Many of the standard dyes may be employed such, for example, as Alizarine Cyanone Green G Extra, Alizarine Sapphire B-N, Alizarine Blue GRL Concentrate, Buffalo Black 3G, Cloth Red B. A satisfactory dye bath consists of A to /z oz. of the dye and gram of wetting agent (Alkanol) to a gallon of water. During the dyeing operation the bath is preferably maintained at a temperature of approximately 160 F. and is continuously agitated. Usually two minutes is suflicient to secure a uniform dyeing of the article under the-conditions above described. If the article has been subjected to a plurality of treatments so as to provide a heavy deposit of the hydrous oxide, a single dyeing treatment following the final precipitation treatment may suffice, but if desired a dyeing treatment may follow each deposition of the hydrous oxide.

After the dyeing treatment the article is given a quick rinse in water at a temperature of 160 to Further'examples of treatments adapted to de-- v If it be desired to color the article, it may be .tralized, and following this posit a fiocculent precipitate capable of being dyed are as follows:

Example 2 A cleaned article is first immersed in a treating solution comprising 10% lead acetate, and then partially dried, after which it is exposed for approximately V minute to ammonia fumes, thereby to effect a precipitation of hydrous lead oxide within the interstices of the protective coating. The treated article may then be rinsed in water at 160 F. and dried in the manner above described;

Example 3 The article to be treated is immersed in a 10% solution of cadmium chloride, dried and then immersed in 8. 10% solution of sodium bicarbonate for about 30 seconds, after which it may be washed and dried.

Example 5 The article may first be dipped in a 20% silver nitrate solution, then dried and fixed by immersion in a solution of potassium iodide, after which the article is rinsed and dried.

Example 6 Example 7 The article to be treated is first immersed in a 10% solution of nickel acetate at room temperature and following this treatmentthe article is immersed in a solution of dimethylglyoxime solution. The precipitate deposited within the interstices of the protective coating produces a brown color.

: Example 10 The article may be immersed in a 10% lead acetate solution, after which it is immersed in a potassium permanganate solution which causes a deposition of a precipitate within the interstices of the protective coating, producing a dark ma hogany color.

In each of the above Examples 7 to 10, the article may be rinsed and dried after the precipita=- tion treatment, and if desired a supplementary coating may be provided in the manner previously described.

If it be desired to treat an article having a nonhomogeneous surface, such as an article havin soldered,- brazed or welded parts, or an article having brass, copper or the like inserts, such an article may first beplated with zinc, cadmiurp og;

' other material capable of providing a surface which is effective to precipitate nickel dimethylglyoxime within the interstices of the protective coating, thus producing a scarlet color.

Example 8 The article may be dipped in a 21% solution of potassium dichromate at 125 F. and following this treatment the article is immersed in lead acetate solution of approximately the same concentration and maintained at about 125 F.- A precipitate of lead chromate is deposited within the interstices of the protective coating and produces a canary yellow coloration.

Example 9 The article may be immersed in a 20% magnesium' sulphate solution, previously slightly neutreatment the article is immersed in a partially saturated tannic acid phosphates and oxalates,

pregnating said crystalline surface and penetratwhich may be subsequently treated with a phosphate conversion process such as Bonderizing, or other method effective to produce a relatively porous, crystalline surface, after which th treated article may be processed in accordance with any of the foregoing procedures.

The present invention not only increases the resistance of an article to corrosion, but has been found to be of great advantage in coloringparts for the purpose of identification, such as machine elements, fittings, etc., since the treatment does not produce appreciable dimensional changes, in contrast to coloring by the use of coating compositions. Accordingly, accurately fitting parts may not only be rendered resistant to corrosion, but also provided with a distinct and uniform coloration without impairing their use.

While I have disclosed different illustrative procedures for increasing the resistance to corrosion and simultaneously coloring different types of articles, it is to be understood that the invention is generally applicable both to ferrous and non-ferrous articles which have or 'are capable of receiving a relatively insoluble, porous, crystalline surface, and it is to be further understood that various modifications in procedure, as well as the substitution of the equivalent reagents. for those herein suggested, may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

l. The method of treating a metallic article having a protective coating consisting essentially of an insoluble porous crystalline surface'in the form of ametallic salt of the group consisting of which comprises iming the interstices thereof with an aqueous solution of a metallic salt efiective to yield an insoluble gelatinous precipitate containing water adsorbed by its component particles (as distinguished from a precipitate in which water is chemically combined in definite stoichiometric proportionsl thereafter subjecting the impreg-' nated surface to such a treatment as evaporation, cooling, heating, chemical action or dilution which is effective to precipitate the insoluble precipitate from said solution, and at least partially dehydrating the precipitated material so as I to produce a relatively insoluble protective dcposit within the interstices of said crystalline surface.

2. The method in accordance with claim 1 in which the metallic salt is effective to yield an hydrous oxide precipitate.

3. The method in accordance with claim 1 in which the metallic salt is efl'ective to yield a colored insoluble gelatinous precipitate.

4. The method in accordance with claim 1 including the step of dyeing the deposited precipitate within said interstices.

5. The method in accordance with claim 1 in which the metallic salt is an aluminum compound etiective to yield an hydrous aluminum oxide precipitate.

8. The method in accordance with claim l in .which the metallic salt is a lead compound efl'ective to yield an hydrous lead compound precipitate.

7. The method in accordance with claim 1, in which the metallic salt is a zinc compound eflective to yield an hydrous zinc compound precipitate.

8. A product prepared by the method 01 JAMES N. TU'I'I'LE.

10 claim 1. 

